Structure to achieve high-Q and low insertion loss film bulk acoustic resonators

ABSTRACT

A film bulk acoustic resonator is formed on a substrate. The film bulk acoustic resonator includes a layer of piezoelectric material having a first surface proximate the substrate, and a second surface distal from the substrate. The first conductive layer deposited on the first surface of the piezoelectric material includes a first portion having a surface on a different plane than a surface associated with a second portion.

This application is a divisional of U.S. application Ser. No. 10/716,750filed Nov. 19, 2003 now U.S. Pat. No. 6,861,783 which is a divisional ofU.S. patent application Ser. No. 10/023,594, filed on Dec. 17, 2001. nowU.S. Pat. No. 6,662,419 These applications are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention pertains to forming a film bulk acoustic resonator(“FBAR”) structure. More specifically, the present invention relates tothe methods of forming a structure for a film bulk acoustic resonatorhaving high-Q and low insertion loss.

BACKGROUND OF THE INVENTION

In some instances it is desirable to provide a radio frequency front-endfilter. In the past ceramic filters and SAW filters have been used asfront-end radio frequency filters. There are problems with SAW filtersin that such filters start to have excessive insertion loss above 2.4gigahertz (GHz). Ceramic filters are large in size and can only befabricated with increasing difficulty as the frequency increases.

A basic FBAR device 100 is schematically shown in FIG. 1. The FBARdevice 100 is formed on the horizontal plane of a substrate 110. A firstlayer of metal 120 is placed on the substrate 110, and then apiezoelectric layer 130 is placed onto the metal layer 120. Thepiezoelectric layer can be ZnO, AIN, PZT, any other piezoelectricmaterials. A second layer of metal 122 is placed over the piezoelectriclayer 130. The first metal layer 120 serves as a first electrode 120 andthe second metal layer 122 serves as a second electrode 122. The firstelectrode 120, the piezoelectric layer 130, and the second electrode 122form a stack 140. A portion of the substrate 110 behind or beneath thestack 140 is removed using back side bulk silicon etching. The back sidebulk silicon etching is done using deep trench reactive ion etching orusing a crystallographic-orientation-dependent etch, such as KOH, TMAH,and EDP. Back side bulk silicon etching produces an opening 150 in thesubstrate 110. The resulting structure is a horizontally positionedpiezoelectric layer 130 sandwiched between the first electrode 120 andthe second electrode 122 positioned above the opening 150 in thesubstrate. The FBAR is a membrane device suspended over an opening in ahorizontal substrate.

FIG. 2 illustrates the schematic of an electrical circuit 200 whichincludes a film bulk acoustic resonator 100. The electrical circuit 200includes a source of radio frequency “RF” voltage 210. The source of RFvoltage 210 is attached to the first electrode 120 via electrical path220 and attached to the second electrode 122 by the second electricalconductor 222. The entire stack 140 can freely resonate in the Zdirection “d₃₃” mode when the RF voltage at resonant frequency isapplied. The resonant frequency is determined by the thickness of themembrane or the thickness of the piezoelectric layer 130 which isdesignated by the letter “d” or dimension “d” in FIG. 2. The resonantfrequency is determined by the following formula:

f₀˜V/2d, where

f₀=the resonant frequency,

V=acoustic velocity of piezoelectric layer, and

d=the thickness of the piezoelectric layer.

It should be noted that the structure described in FIGS. 1 and 2 can beused either as a resonator or as a filter. To form an FBAR,piezoelectric films, such as ZnO and AlN, are used as the activematerials. The material properties of these films, such as thelongitudinal piezoelectric coefficient and acoustic loss coefficient,are key parameters for the resonator's performance. Key performancefactors include Q-factors, insertion loss, and the electrical/mechanicalcoupling. Currently, to manufacture an FBAR the piezoelectric film isdeposited on a metal electrode using reactive sputtering. The resultingfilms are polycrystalline with a c-axis texture orientation. In otherwords, the c-axis is perpendicular to the substrate. This processingprocedure has several problems.

An FBAR is formed as a piezoelectric layer sandwiched between twoelectrodes. Top and bottom electrodes are necessary for electricaloutpur of the FBAR Therefore a bottom electrode is required. Thestarting layer or seed layer for the piezoelectric film deposition forFBAR has been limited to conductive materials. Any other non-conductiveor single-crystal materials, which could induce very high-quality orsingle-crystal piezoelectric films, can not be used as the seed layerusing conventional FBAR fabrication techniques.

When a piezoelectric film is sputtered onto a conductive metal, theinitial layer of approximately 0.05 um of the sputtered film typicallyconsists of a polycrystalline material with partially developed texture.This initial layer has poor piezoelectric effect. This degrades theoverall film quality. This becomes a performance issue for highfrequency FBARs having a resonance frequency of 10 GHz or above whichhas a piezoelectric film about 0.2 um thick.

Thus, there is need for an FBAR device and a method for producing anFBAR device that results in a single-crystal piezoelectric film. Thereis also a need for a method of fabricating an FBAR device that has goodperformance qualities and which uses a seed layer other than a highlyconductive electrode. There is also a need for a fabrication techniquewhere an initial sputtered layer of piezoelectric material can beremoved since this layer may be polycrystalline and have poorpiezoelectric effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.However, a more complete understanding of the present invention may bederived by referring to the detailed description when considered inconnection with the figures, wherein like reference numbers refer tosimilar items throughout the figures and:

FIG. 1 illustrates a cross sectional view of a prior art film bulkacoustic resonator.

FIG. 2 illustrates a schematic of an electrical circuit of a film bulkacoustic resonator.

FIG. 3A illustrates a top view of a single crystal substrate with adielectric layer and a portion of a first electrode thereon.

FIG. 3B illustrates a side view of a substrate or wafer shown in FIG.3A.

FIG. 4A illustrates a substrate after a piezoelectric film and secondelectrode have been deposited on the substrate.

FIG. 4B illustrates a side view of a substrate shown in FIG. 4A.

FIG. 5A illustrates a substrate after a portion of the substratematerial beneath the piezoelectric material has been removed.

FIG. 5B illustrates a side view of a substrate shown in FIG. 5A.

FIG. 6A illustrates a substrate after a portion of the seed layerbeneath the piezoelectric material has been removed.

FIG. 6B illustrates a side view of a substrate shown in FIG. 6A.

FIG. 7A illustrates a substrate after a second portion of the firstelectrode is deposited on the piezoelectric layer and on the firstportion of the first electrode.

FIG. 7B illustrates a side view of a substrate shown in FIG. 7A.

FIG. 8A illustrates a top view of a substrate with a non-conductive seedlayer and a portion of a first electrode thereon.

FIG. 8B illustrates a side view of a substrate shown in FIG. 8A.

FIG. 9A illustrates a substrate after a piezoelectric film and a secondelectrode has been deposited thereon.

FIG. 9B illustrates a side view of a substrate shown in FIG. 9A.

FIG. 10A illustrates a substrate after a portion of the substratematerial beneath the piezoelectric material has been removed.

FIG. 10B illustrates a side view of a substrate shown in FIG. 10A.

FIG. 11A illustrates a substrate after a portion of the seed layerbeneath the piezoelectric material has been removed.

FIG. 11B illustrates a side view of a substrate shown in FIG. 11A.

FIG. 12A illustrates a substrate after a second portion of the firstelectrode is deposited on the piezoelectric layer and on the firstportion of the first electrode.

FIG. 12B illustrates a side view of a substrate shown in FIG. 12A.

FIG. 13A illustrates a top view of a substrate with a seed layer and aportion of a first electrode thereon.

FIG. 13B illustrates a side view of a substrate shown in FIG. 13A.

FIG. 14A illustrates a substrate after a piezoelectric film has beendeposited thereon.

FIG. 14B illustrates a side view of a substrate shown in FIG. 14A.

FIG. 15A illustrates a substrate after a second electrode has beendeposited on the piezoelectric film and after a portion of the substratehas been removed from the back side of the substrate.

FIG. 15B illustrates a side view of a substrate shown in FIG. 15A.

FIG. 16A illustrates a substrate after a portion of the substrate, and aportion of the seed layer beneath the piezoelectric material, and aportion of the piezoelectric material have been removed.

FIG. 16B illustrates a side view of a substrate shown in FIG. 16A.

FIG. 17A illustrates a substrate after a second portion of the firstelectrode is deposited on the piezoelectric layer and on the firstportion of the first electrode.

FIG. 17B illustrates a side view of a substrate shown in FIG. 17A.

FIG. 18A illustrates a top view of a substrate with a dielectric film, aconductive seed layer, and a portion of a first electrode thereon.

FIG. 18B illustrates a side view of a substrate shown in FIG. 18A.

FIG. 19A illustrates a substrate after a piezoelectric film has beendeposited thereon.

FIG. 19B illustrates a side view of a substrate shown in FIG. 19A.

FIG. 20A illustrates a substrate after a second electrode has beendeposited on the piezoelectric film and after a portion of the substratehas been removed from the back side of the substrate.

FIG. 20B illustrates a side view of a substrate shown in FIG. 20A.

FIG. 21A illustrates a substrate after a portion of the substrate, and aportion of the dielectric layer, a portion of the seed layer beneath thepiezoelectric material, and the poorly oriented piezoelectric materialhave been removed.

FIG. 21B illustrates a side view of a substrate shown in FIG. 21A.

FIG. 22A illustrates a substrate after a second portion of the firstelectrode is deposited on the piezoelectric layer and on the firstportion of the first electrode.

FIG. 22B illustrates a side view of a substrate shown in FIG. 22A.

The description set out herein illustrates the various embodiments ofthe invention and such description is not intended to be construed aslimiting in any manner.

DETAILED DESCRIPTION

Described in FIGS. 3A–22B are the various process steps used to make oneof several embodiments of the inventive film bulk acoustic resonator“FBAR.”

One embodiment of the invention is discussed with reference to FIGS.3A–7B. FIGS. 3A and 3B illustrate a top and side view of a singlecrystal substrate 300 with a single crystal seed layer 310 and adielectric layer 320. A first portion of a first electrode 400 is formedon a portion of the seed layer 310 and on a portion of the dielectriclayer 320. The single crystal substrate 300 can be silicon or siliconcarbon (Si, or SiC). The single crystal seed layer 310 is needed tofacilitate single crystal piezoelectric film growth. It should beunderstood that if the single crystal substrate 300 is capable offacilitating the single crystal piezoelectric film growth, the singlecrystal seed layer 310 may not be needed. The dielectric layer 320 isneeded for isolation or prevention of a metal reaction with the seedlayer 310 or a metal reaction with the substrate 300. The dielectriclayer 320 is patterned to open a window 322. The window exposes thesingle crystal seed layer 310 so that a piezoelectric film can be grownon the exposed portion of the single crystal seed layer 310. After thewindow 322 has been formed in the dielectric layer 320, the firstportion of the first electrode 400 is formed so that it covers a portionof the single crystal seed layer 310 within the window 322, so that itcovers a portion of the dielectric layer 320. The first portion of thefirst electrode 400 may also be termed as a buried metal trace and willbe used to make electrical contact with the device, as will be shown anddiscussed with respect to FIGS. 7A and 7B.

FIGS. 4A and 4B illustrate top and side views, respectively, of thesubstrate 300 after a piezoelectric film 410 and a second electrode 420have been deposited on the substrate 300. Initially, a single crystalpiezoelectric film 410 is deposited and patterned so that it isdeposited within the window 322 where the single crystal seed layer 310is exposed. The single crystal piezoelectric film 410 has a firstsurface 412 which is formed in contact with the single crystal seedlayer 310. The first surface of the single crystal piezoelectric film410 is in close proximity to the substrate 300. The single crystalpiezoelectric film 410 also includes a second surface 414 which isremote from the single crystal substrate 300.

After the piezoelectric film 410 is formed and patterned, a secondelectrode 420 is deposited and patterned. The second electrode 420includes a first portion 422 and a second portion 424. The secondportion 424 is deposited over the second surface 414 of thepiezoelectric crystal 410. The first portion 422 of the second electrode420 is deposited on the dielectric layer 320 and also makes electricalcontact with the second portion 424 of the second electrode 420. Inother words, the first portion of the second electrode 420 includes anelectrical contact pad and a portion which is deposited on the sidewallof the piezoelectric film 410. The first portion 422 of the secondelectrode 420 also includes a portion that is deposited on the secondsurface 414 of the piezoelectric crystal 410 so that the first portionis in electrical communication with the second portion 424 of the secondelectrode 420. The second electrode 420 may also be termed as the topelectrode of the FBAR device formed.

FIGS. 5A and 5B illustrate top and side views respectively of thesubstrate 300 after a portion of the substrate material beneath thepiezoelectric layer and the seed layer 310 have been removed. Removing aportion of the substrate 300 produces an opening 500 on the back side ofthe substrate. The substrate material 300 that is removed corresponds tothe portion of the substrate 300 which is under the active area of thefinal device or FBAR. The substrate material is removed usingdeep-trench reactive-ion etching (DRIE). The etched profile of the DRIEis adjusted to be negative so as to produce a first sloped sidewall 502and a second sloped sidewall 504.

FIGS. 6A and 6B illustrate the substrate after a portion of the seedlayer 310 beneath the piezoelectric film 410 has been removed. Thesingle crystal seed layer 310 is etched from the back side of the waferthrough the previously etched DRIE window or opening 500 formed when thesubstrate material 300 was removed from the back side of the wafer. Theetch for removing the single crystal seed layer 310 is self aligned andis stopped on the piezoelectric layer 410 by end point detection. Morespecific, the etch for removing the single crystal seed layer 310 stopsat or near the first surface 412 of the piezoelectric layer 410. Theetch to remove the single crystal seed layer 310 exposes thepiezoelectric layer 410 and specifically surface 412 along the back sideof the substrate. This etch can be said to form a second window 600which is bounded by the single crystal seed layer 310 and exposes thesurface 412 of the piezoelectric crystal 410 at the back side of thesubstrate 300.

FIGS. 7A and 7B show top and side views of the substrate after a secondportion 700 of the first electrode is deposited on the first surface 412of the piezoelectric film 410. The bottom electrode metal is depositedfrom the back side of the wafer. Depositing metal from the back side ofthe wafer or substrate 300 produces the second portion 700 of the firstelectrode. The back side surface of the substrate 300 is also metallizedas is shown by metal layers 710 and 712 in FIG. 7B. The second electrode700 makes electrical contact with the first portion of the firstelectrode 400 or what is also known as the buried metal trace. It shouldbe noted that there is no metal deposited on the sidewalls of theopening 500. When the opening 500 was made, the DRIE was adjusted to benegative thereby producing sloping sidewalls 502 and 504. When the metallayer is deposited which forms the second portion 700 of the firstelectrode, the sloped sidewalls prevent deposit of metal on thesidewalls 502, 504. This prevents a continuous metal layer being formedover all the bulk silicon substrate 300 and provides for a separateelectrode 700 which covers most of the first surface 412 of thepiezoelectric film 410. It should be noted that the first portion 400 ofthe first electrode and the second portion 700 of the first electrodeform the first electrode. Typically the second portion 700 of the firstelectrode overlaps the first portion 400 of the first electrode by anamount to provide adequate electrical connection between the firstportion 400 and the second portion 700 of the first electrode. As shown,the overlapping is approximately 10 micrometers.

Now turning to FIGS. 8A to 12B, a second embodiment and method forforming an FBAR having high Q and low insertion loss will be discussed.In the second embodiment, fabrication procedures that enable using anonconductive seed layer for a piezoelectric film deposition will bediscussed. FIGS. 8A and 8B illustrate a top and side view, respectively,of a substrate 800 having a nonconductive seed layer 810 and a firstportion 1210 of a first electrode 1200 (the entire first electrode isshown in FIG. 12B). The seed layer 810 can be any nonconductive materialwhich can induce a high-quality piezoelectric film when deposited on theseed layer 810. Advantageously, the particular seed layer 810 used onthe substrate 800 is not limited to conductive material. Therefore theseed layer 810 can be selected to optimize particular qualities of apiezoelectric film or layer that is grown upon the seed layer. A metallayer is deposited and patterned onto the seed layer. The metal layerforms a first portion 1210 of a first electrode or bottom electrodecontact. The metal layer 1210 may also be termed as a buried metal traceand includes a first portion 1214 and a second portion 1216. The secondportion 1216 is an electrical contact pad.

FIGS. 9A and 9B illustrate top and side views of the substrate 800 aftera piezoelectric film 910 has been deposited upon the seed layer 810 andafter a second electrode 920 has been deposited and patterned on theseed layer and on the piezoelectric film. A single crystal piezoelectricfilm 910 is deposited and patterned on the seed layer 810. The seedlayer 810 is any nonconductive material which induces the deposit ofhigh-quality piezoelectric films on the seed layer. The piezoelectricfilm 910 includes a first surface 912 which is proximate the substrate800. The first surface 912 actually contacts or interfaces with the seedlayer 810. The piezoelectric film 912 also includes a second surface 914which is remote from the substrate 800. The second electrode 920includes a first portion 922 and a second portion 924. The secondportion 924 is deposited on the second surface 914 of the piezoelectricfilm 910. The second portion 924 covers most of the second surface 914of the piezoelectric film or layer 910. The first portion 922 of thesecond electrode 920 includes a pad 916 and an electrical trace 918. Theelectrical trace 918 electrically connects the pad 916 and the secondportion 924 of the second electrode. Therefore, the trace 918 has aportion that is deposited upon the surface 914 of the second surface 914of the piezoelectric layer 910. The trace 918 also is deposited upon thesidewall or vertical surface of the piezoelectric film 910. The topelectrode or second electrode 920 is deposited and then patterned toform the first portion 922 and the second portion 924.

FIGS. 10A and 10B illustrate the substrate 800 after a portion of thesubstrate material beneath the piezoelectric film 910 has been removed.As best illustrated by FIG 10B, the silicon substrate underpiezoelectric film 910 is removed using deep-trench reactive-ion etching(DRIE). Removing a portion of the silicon substrate 800 from the backside of the substrate 800, produces an opening 1000. The opening 1000can also be termed a DRIE etch window. The etch profile of the DRIEwindow or opening 1000 is adjusted to be negative. The negative etchedprofile of the opening or DRIE window 1000 produces a first slopedsidewall 1002 and a second sloped sidewall 1004.

FIGS. 11A and 11B illustrate the substrate or the device after a portionof the seed layer beneath the piezoelectric material or beneath thepiezoelectric film 910 has been removed. The nonconductive seed layer810 is etched or removed from the back side of the substrate through thepreviously etched DRIE window or opening 1000. The etch is self alignedand effectively stops on the piezoelectric layer 910 by end pointdetection. Specifically, the etch stops at or near the first surface 912of the piezoelectric layer or film 910. The result of the etch from theback side that removes the nonconductive seed layer 810 is an opening1100 in the seed layer 810. The opening 1100 exposes surface 912 of thepiezoelectric film or layer 910 as well as part of the portion 1214 ofthe first portion 1210 of the first electrode.

FIGS. 12A and 12B illustrate top and side views, respectively, of thesubstrate after the back side of the substrate 800 is metallized. Metalis deposited on the back side of the wafer. The deposited metal form thesecond portion 1212 of the first electrode 1200 as well as metallizedlayers 1220 and 1222 on the back side of the substrate 800. The opening1000 or DRIE window which was previously adjusted to have a negativeprofile and to produce sloping sidewalls 1002 and 1004 prevents depositof the metal on the sidewalls 1002, 1004. This in turn prevents acontinuous metal layer being formed on the bulk silicon substrate sothat the second portion 1212 of the first electrode 1200 is separatedfrom the other metallized portions 1220 and 1222. The second portion1212 of the first electrode 1200 contacts the first portion 1210 of thefirst electrode. The first portion 1210 and the second portion 1212 ofthe first electrode 1200 overlap so that electrical contact is madebetween the first and second portions. In this particular embodiment,the overlap is approximately 12 micrometers.

Now turning to FIGS. 13A–17B, a third embodiment of the invention willbe discussed. In the third embodiment, a structure and fabricationprocedure to enable removal of an initial piezoelectric film of poorquality is discussed. FIGS. 13A and 13B illustrate a side view and topview, respectively of a substrate 1300 having a nonconductive seed layer1310 and a first portion 1710 of a first electrode 1700 (the entirefirst electrode is shown in FIG. 17B). The starting seed layer 1310 isfirst deposited upon the substrate 1300. The seed layer may be adielectric material or any other nonconductive material chosen so that agood quality piezoelectric film will be formed when the piezoelectricmaterial or film is deposited onto the seed layer 1310. It should benoted that the substrate 1300 itself could be used as the nonconductive“seed layer.” The metal layer or first portion 1710 of the firstelectrode is deposited and patterned for later contact with a secondportion of the first electrode. The first electrode portion 1710includes a contact pad 1716 and an electrical trace 1714. The firstportion 1710 of the first electrode may also be termed as a buried metaltrace.

FIG. 14A and FIG. 14B illustrate top and side views of the substrate1300 after the piezoelectric film 1410 has been deposited on the seedlayer 1310 of the substrate 1300. The piezoelectric material isdeposited and patterned to form the piezoelectric film 1410. Thepiezoelectric film 1410 includes a first surface 1412 which is proximatethe substrate 1300 and includes a second surface 1414 which is distal orremote from the substrate 1300. The initial layers 1420 of the depositedfilm may have a poor texture. The initial layers of the film are denotedby the reference numeral 1420. The initial layers of the piezoelectricfilm 1410 are approximately 0.05 micrometers in thickness. After theinitial layers of poor texture piezoelectric material, designated by thereference numeral 1420, the piezoelectric material then starts growingin C-axis oriented texture, as depicted by reference numeral 1422. Theinterface between the poor texture area 1420 and the volume ofpiezoelectric material that grows in C-axis oriented texture 1422 hasbeen designated by the reference numeral 1421.

FIGS. 15A and 15B illustrate the substrate after a second electrode 1520has been deposited on the substrate 1300 and after a portion of thesubstrate 1300 has been removed from the back side of the substrate1300. After the piezoelectric film 1410 has been deposited onto the seedlayer 1310 of the substrate 1300, a second electrode 1520 is depositedand patterned. The second electrode includes a first portion 1522 and asecond portion 1524. The second portion 1524 covers or substantiallycovers the surface 1414 of the piezoelectric film 1410. The firstportion 1522 of the second electrode 1520 includes a pad 1516 and anelectrical contact or trace 1518 which connects the pad 1516 to thesecond portion 1524 of the second electrode 1520. The trace 1518 isdeposited upon the sidewall of the piezoelectric film 1410, on the seedlayer 1310 and on the second surface 1414 of the piezoelectric film1410. As mentioned previously, the trace 1518 provides electricalcontact between the first portion 1522 and the second portion 1524 ofthe second electrode 1520.

As best seen in FIG. 15B, the silicon substrate 1300 beneath thepiezoelectric film 1410 has been removed by deep-trench reactive-ionetching (DRIE). Removal of the substrate portion beneath thepiezoelectric film 1410 creates an opening 1500 which also may bereferred to as a DRIE window. The etched profile of the DRIE window oropening 1500 is adjusted to be negative, thereby producing a firstsloped sidewall 1502 and a second sloped sidewall 1504.

FIGS. 16A and 16B illustrate the substrate 1300 after a portion of thesubstrate, a portion of the seed layer 1310 and a portion of thepiezoelectric material 1420, have been removed from the back sidesurface of the substrate 1300. A portion of the seed layer 1310 and aportion of the poorly oriented piezoelectric layer 1420 are etched fromthe back side of the substrate 1300 through the previously etchedopening 1500 or DRIE window. The etch is self aligned. The etching ofthe seed layer can effectively stop on the piezoelectric layer 1410 byend point detection. The etching of the poorly oriented piezoelectricfilm or films 1420 is based on time control. In other words, a DRIE etchremoves material at a certain rate. Therefore, for a given amount oftime, a given amount of material is generally removed. The etch forremoving a portion of the seed layer 1310 and a portion of the poorlyoriented piezoelectric layer 1420 is conducted so that the entirethickness of the poorly oriented piezoelectric layer 1420 is removed andyet so that not all of the thickness of the first portion 1710 of thefirst electrode is removed. The etch is conducted until the interfacebetween the poorly oriented piezoelectric layer 1420 and the C-axisoriented portion 1422 of the piezoelectric film 1410 is either just metor slightly passed. In other words, after the etching is complete, onlyC-axis oriented film 1422 remains.

FIGS. 17A and 17B show top and side views, respectively, of thesubstrate 1300 after a second portion 1712 of the first electrode 1700has been deposited from the back side of the substrate 1300 onto theC-axis oriented portion 1422 of the piezoelectric film 1410. The backside of the substrate 1300 is metallized resulting in the second portion1712 of the first electrode being deposited through the DRIE windowpreviously formed. Metal is deposited on the entire back side of thesubstrate which also produces metallized films or portions 1720 and1722. The second portion 1712 and the first portion 1710 form the firstelectrode 1700. The second portion 1712 of the first electrode 1700overlaps the first portion 1710 of the first electrode by approximately10 micrometers so that electric contact is made between the firstportion 1710 and the second portion 1712. It should be noted that thereis no metal deposited upon the sidewalls 1502 and 1504 of the opening1500 due to the fact that the DRIE previously performed was adjusted tobe negative. As a result the bottom electrode or second portion 1712 ofthe first electrode 1710 is prevented from forming a continuous metalfilm across the entire back side of the substrate 1300. The advantage ofthis particular embodiment is that the poorly oriented film portion 1420is removed so that the FBAR formed by the piezoelectric layer 1410 andthe first electrode 1700 and the second electrode 1520 only have C-axisoriented piezoelectric material between the electrodes. This forms anFBAR device having desirable qualities of high Q and low insertion loss.

Now turning to FIGS. 18A–22B, a fourth embodiment of the invention willbe discussed. In the fourth embodiment, a structure and fabricationprocedure that enables the removal of initial piezoelectric film of poorquality is discussed. In this embodiment, the seed layer is formed of aconductive material. FIGS. 18A and 18B show top and side views of asubstrate 1800 having a dielectric film 1810, a conductive seed layer1820 and a first portion 2210 of a first electrode 2200 (the entirefirst electrode is shown in FIG. 22B) deposited on the substrate 1800.The dielectric layer or film 1810 is initially deposited on thesubstrate 1800 to provide for isolation between the substrate 1800 andthe conductive seed material 1820 and the first portion 2210 of thefirst electrode. The conductive seed layer material 1820 is thendeposited onto the dielectric layer 1810. The seed layer is patterned sothat it is of the appropriate size to receive a piezoelectric materialfor an FBAR device. A metal layer is deposited and patterned to form thefirst portion 2210 of a first electrode. The first portion 2210 of thefirst electrode may be termed as a buried metal trace which will be usedto form electrical contact with a second portion of the first electrode.It should be noted that the metal layer that is used to form the firstportion 2210 of the first electrode could be of the same material as theseed layer 1820. The first portion 2210 of the first electrode includesa pad 2216 and a an electrical trace 2214.

FIGS. 19A and 19B show top and side views, respectively, of thesubstrate 1800 after a piezoelectric film 1910 has been depositedthereon. The piezoelectric material 1910 is deposited and patterned. Thedeposited film 1910 includes a portion which has poor texture 1920 and aportion that has C-axis oriented texture 1922. The poor texture portionof the piezoelectric material is non C-axis oriented. The deposited filmof poor texture is generally the initial layers comprising approximately0.05 microinches. A line, carrying the reference numeral 1921 is shownin FIG. 19B and depicts the transition between the portion of thedeposited piezoelectric film having poor texture 1920 and the portion ofthe piezoelectric film having C-axis oriented texture 1922.

FIGS. 20A and 20B show top and side views, respectively after a secondelectrode 2020 has been deposited upon the piezoelectric film 1910 andafter a portion of the substrate 1800 has been removed from the backside surface of the substrate 1800. Initially, the second electrode 2020is deposited and patterned. The second electrode 2020 can also be termedas the top electrode in the FBAR device. The second electrode 2020includes a first portion 2022 and a second portion 2024. The secondportion 2024 substantially covers the surface 1914 of the piezoelectricfilm 1910. The first portion 2022 of the second electrode 2020 includesa contact pad 2016 and a trace 2018 that connects the contact pad 2016and the second portion 2024 of the second electrode 2020. The substratematerial underneath the piezoelectric film 1910 is removed bydeep-trench reactive-ion etching (DRIE). The removal of the portion ofthe substrate 1800 produces an opening 2000 having sidewalls 2002 and2004. The etched profile of the DRIE is adjusted to be negative. Theopening 2000 can also be termed as a DRIE etch window. Only silicon orthe substrate material 1800 is removed. Therefore, the opening or DRIEetch window 2000 is bounded by sidewalls 2002, 2004 and the dielectriclayer 1810.

FIGS. 21A and 21B illustrate the substrate after a portion of thesubstrate 1800, a portion of the dielectric layer 1810, a portion of theseed layer 1820 and the poorly oriented piezoelectric material 1920 havebeen removed. The portion of the dielectric material 1810, a portion ofthe metal seed layer 1820 and the poorly oriented piezoelectric layer1920 are etched from the back side of the substrate 1800 through thepreviously etched DRIE window or opening 2000. The etch is self aligned.The etching of the seed layer 1820 can effectively stop on thepiezoelectric layer 1910 by end point detection. The etching of thepoorly oriented piezoelectric films or film 1920 is based on timecontrol. After the poorly oriented piezoelectric film or films 1920 havebeen removed, only C-axis oriented film 1922 remains as part of thepiezoelectric film 1910. As a result, the piezoelectric properties ofthe deposited film 1910 are improved.

FIGS. 22A and 22B illustrate top and side views after a second portion2212 of the first electrode 2200 is deposited along with othermetallized portions on the first portion 2210 of the first electrode2200. Metal is deposited on the back side of the substrate 1800 formingmetallized portions 2220, 2222 and the second portion 2212 of the firstelectrode 2200. Since the etched profile of the DRIE window or opening2000 was adjusted to be negative in the previous step, metallizing ordepositing metal on the back side surface of the substrate 1800 does notresult in metal deposits on the sidewalls 2002, 2004 of the opening2000. The second portion 2212 of the first electrode 2200 is placed inelectrical contact with the first portion 2210 of the first electrode2200. There is an amount of overlap between the first portion 2210 andthe second portion 2212 of the first electrode 2200 so as to provide anadequate electrical path between the first and second portions. In thisparticular embodiment, the overlap is approximately 10 micrometers. Theresult of this procedure is that a high-quality FBAR device can beformed even though the piezoelectric material or film 1910 is formed ona conductive seed layer 1820. The result of this procedure is that thepoor texture film or films of piezoelectric material are removed by backside etching, leaving only C-axis oriented piezoelectric material 1922as part of the FBAR device.

The structures shown and described in the above figures and the methodsdiscussed for making these structures provides many advantages. Usingthe inventive method, FBAR devices having a single-crystal piezoelectricfilm can be obtained. A further advantage is that any seed film can beused, rather than being forced to use the conductive metal material forthe bottom or first electrode. The seed material can be selected toproduce a piezoelectric film having a particular quality or qualities.In addition, even if the initial layer of a piezoelectric film hasundesirable qualities, it can be removed to form an FBAR having high-Qand low insertion loss. The result is an FBAR that has good performancequalities when used in high frequency applications.

The foregoing description of the specific embodiments reveals thegeneral nature of the invention sufficiently that others can, byapplying current knowledge, readily modify and/or adapt it for variousapplications without departing from the generic concept, and thereforesuch adaptations and modifications are intended to be comprehendedwithin the meaning and range of equivalents of the disclosedembodiments.

It is to be understood that the phraseology or terminology employedherein is for the purpose of description and not of limitation.Accordingly, the invention is intended to embrace all such alternatives,modifications, equivalents and variations as fall within the spirit andbroad scope of the appended claims.

1. A film bulk acoustic resonator device formed on a substrate having anopening therein, the film bulk acoustic resonator comprising: a seedlayer of non conductive material; and a layer of piezoelectric materialcontacting the seed layer of non-conductive material, wherein theopening extends through the substrate and the seed layer.
 2. A film bulkacoustic resonator device formed on a substrate having an openingtherein, the film bulk acoustic resonator comprising: a seed layer ofnon conductive material; and a layer of piezoelectric materialcontacting the seed layer of non-conductive material, wherein the seedlayer also has an opening therein that corresponds to the opening in thesubstrate, the opening in the seed layer including a layer of conductivematerial.
 3. The film bulk acoustic resonator of claim 2 wherein theconductive material within the opening in the seed layer is a portion ofa first electrode associated with a first surface of the layer ofpiezoelectric material.
 4. The film bulk acoustic resonator of claim 3further comprising a second electrode associated with a second surfaceof the layer of piezoelectric material.
 5. The film bulk acousticresonator of claim 4 further comprising a source of RF voltage attachedbetween the first electrode and the second electrode.
 6. A film bulkacoustic resonator device formed on a substrate having an openingtherein, the film bulk acoustic resonator comprising: a seed layer; anda layer of piezoelectric material contacting the seed layer ofnon-conductive material, wherein the opening extends through thesubstrate and through at least a portion of the seed layer.
 7. A filmbulk acoustic resonator device formed on a substrate having an openingtherein, the film bulk acoustic resonator comprising: a seed layer; anda layer of piezoelectric material contacting the seed layer ofnon-conductive material, wherein the seed layer also has an openingtherein that corresponds to the opening in the substrate, the opening inthe seed layer including a portion of conductive material.
 8. The filmbulk acoustic resonator of claim 7 wherein the portion of conductivematerial within the opening in the seed layer is a portion of a firstelectrode associated with a first surface of the layer of piezoelectricmaterial.
 9. The film bulk acoustic resonator of claim 8 furthercomprising a second electrode associated with a second surface of thelayer of piezoelectric material.
 10. The film bulk acoustic resonator ofclaim 9 further comprising a source of RF voltage attached between thefirst electrode and the second electrode.
 11. The film bulk acousticresonator of claim 6 wherein the seed layer is a single crystal seedlayer.
 12. The film bulk acoustic resonator of claim 6 furthercomprising a dielectric layer contacting the seed layer.
 13. The filmbulk acoustic resonator of claim 12 wherein dielectric layer contacts afirst electrical contact and a second electrical contact.
 14. The filmbulk acoustic resonator device of claim 1 wherein the layer ofpiezoelectric material further comprises: a first surface proximate thesubstrate; and a second surface distal from the surface of thesubstrate.
 15. The film bulk acoustic resonator device of claim 14further comprising: a first conductive layer including a portion incontact with the first surface of the layer of piezoelectric material,the first conductive layer being nonplanar; and a second conductivelayer in contact with the second surface of the layer of piezoelectricmaterial.
 16. The film bulk acoustic resonator device of claim 15wherein the first conductive layer and the second conductive layer aredeposited on the first surface and second surface of the layer ofpiezoelectric material.
 17. The film bulk acoustic resonator device ofclaim 14 wherein the layer of piezoelectric material is a single-crystalfilm.
 18. The film bulk acoustic resonator device of claim 17 whereinthe layer of piezoelectric material is AlN.
 19. The film bulk acousticresonator device of claim 17 wherein the layer of piezoelectric materialis ZnO.
 20. The film bulk acoustic resonator device of claim 17 whereinthe layer of piezoelectric material is a C-axis orientated film.
 21. Thefilm bulk acoustic resonator device of claim 14 wherein the layer ofpiezoelectric material includes: a C-axis oriented portion; and a nonC-axis oriented portion, wherein at least a portion of the firstconductive layer and a portion of the second conductive layer isproximate the C-axis oriented portion of the layer of piezoelectricmaterial.
 22. The film bulk acoustic resonator device of claim 15wherein the first conductive layer includes: a first planar portion; anda second planar portion, the first planar portion and the second planarportion having surfaces in different planes.
 23. The film bulk acousticresonator device of claim 13 the film bulk acoustic resonator positionedover the opening in the substrate.